There has been a growth in demand for packet switched wireless data services due to the growth in internet applications. A typical channel over which these data services are delivered is a radio channel. There are available radio channels in an increasing number of frequency bands. A frequency band of particular interest is the IMT-2000 frequency band (at a frequency of about 2 GHz). This frequency band is used for delivery of data services using wideband code division multiple access (WCDMA) techniques. Two WCDMA techniques that may be used in this frequency band are frequency division duplex (FDD) techniques and time division duplex (TDD) techniques.
A well known feature of radio channels is multipath propagation. Radio waves from a transmitter may take several paths simultaneously to a receiver: these multiple paths are possible due to the radio waves reflecting off various objects in the surroundings. The objects that cause these reflections can either be stationary or mobile (for example, the radio waves may reflect off moving vehicles). Indeed the receiver may be either stationary or mobile. These radio waves combine at the receiver (by the laws of superposition). The combination can be either constructive or destructive. Destructive combination leads to a smaller signal at the receiver whereas constructive combination leads to a larger signal at the receiver.
When either the receiver moves or the surroundings of the receiver move, the receiver will progressively enter zones of constructive and destructive interference. In such a way, the signal strength at the receiver will fade up and down. This fading can be a problem for transmission of mobile data.
There are various strategies for overcoming the problems of fading. It is possible to employ forward error correction to correct errors that occur during a fade. Generally forward error correction requires the errors to be uniformly distributed. This can be achieved using interleaving. The depth of the interleaver is a function of the channel: for fast channels, a small interleaving depth may be employed, for slow channels, a larger interleaving depth is required. For slow channels, the latency associated with a large interleaving depth prohibits its use.
It is possible for the transmitter to base it's transmit power assuming a worst case fade depth. This strategy is wasteful of transmit power.
A strategy that is useful when packet data services are transmitted across a fading radio channel is to exploit multi-user diversity. Multi-user diversity may be employed when there are multiple users that are all requesting service concurrently. If the transmitter knows the channel conditions that are being experienced by the receivers that it is serving, it may schedule those users that are experiencing favourable channel conditions in preference to those experiencing unfavourable channel conditions. Furthermore, the scheduler may wish to use less error correcting coding or transmit using a higher order modulation when transmitting to users with the best channel conditions (such techniques will increase the instantaneous throughput to those users).
In the HSDPA system that is specified by 3GPP, the transmitter is the Node B (a “base station”) and the receiver is the UE (user equipment, i.e., a “remote station”). The HSDPA system that is specified by 3GPP exploits multi-user diversity in several ways:                the amount of error correcting coding and modulation applied may be varied between transmissions (adaptive modulation and coding: AMC).        the scheduling function is located in the Node B: this network element has a shorter round trip delay to the UE than the RNC (Radio Network Controller) which is where the scheduling function is classically located. The Node B may attempt to always choose users to schedule that are experiencing favourable channel conditions.        the UE reports channel quality directly to the Node B, allowing the Node B to make scheduling decisions based on channel quality.        
3GPP have specified HSDPA both for the FDD (Frequency Division Duplex) and for the TDD (Time Division Duplex) modes. In both modes of operation, there is a mechanism by which channel quality estimates are fed back from the UE to the Node B.
In FDD, a dedicated channel exists that runs continuously in the uplink and the downlink. The UE makes measurements on the downlink channel and reports these measurements continuously in the uplink (where the reporting period is specified by the network). This system has the advantage that the Node B is continuously updated with channel quality information from the UE. The disadvantage with this system is that these dedicated channels need to be maintained: these dedicated channels consume scarce power and code resources.
In TDD, there is no requirement for a dedicated channel (in the sense that any dedicated channel that is maintained by the network serves no purpose in the functioning of HSDPA and may be configured to consume an insignificant amount of physical resources in any case). When data-bearing resources (HS-DSCH: High Speed Downlink Shared Channel) are allocated in TDD HSDPA, a shared uplink channel (HS-SICH: High Speed Shared Information Channel) is automatically allocated. This uplink channel carries an acknowledgement of the HS-DSCH and a channel quality indication. The advantage of this system is that a resource-consuming dedicated channel does not need to be maintained. The disadvantage is that channel quality information is received by the scheduler in the Node B only infrequently.
The TDD method of channel quality information reporting can work well with certain traffic models and allocation strategies. Namely, when a streaming traffic model is used, each UE will be continually allocated with a resource (and the Node B will continually receive channel quality reports). However, a streaming traffic model is not ideally suited to exploitation of multi-user diversity (since a minimum “drip-feed” of allocation is required in order to maintain the stream).
A strategy that could be adopted by the Node B to gain channel quality information is for the Node B to explicitly request a channel quality report from the UE. This channel quality request message may be small and thus have an insignificant impact on overall system throughput. The Node B may use the returned channel quality reports to gain multi-user diversity benefits by employing adaptive modulation and coding, fast scheduling and other techniques previously referred to.
Methods for explicitly requesting channel quality information reports from the UE have been proposed. However, these methods of requesting channel quality information require amendments to the 3GPP standards and do not propose how these channel quality information requests would be scheduled by the Node B or how the UE would derive the channel quality information that is to be returned to the UE.
A need therefore exists for HSDPA communication wherein the abovementioned disadvantage(s) may be alleviated.